Semiconductor laser modules have been conventionally used for coupling light emitted from a semiconductor laser to an optical fiber. The semiconductor laser is fixed on a submount, and light emitted from the semiconductor laser is optically coupled with an optical fiber (Japanese Unexamined Patent Application Publication No. 2013-4752 (JP-A-2013-4752), for example).
FIG. 4A is a view showing a conventionally used submount material 100 and FIG. 4B is an enlarged view of a section X in FIG. 4A. The submount material is formed of aluminum nitride (AlN), for example, and a plating layer 101 is formed on a part of a surface thereof. The plating layer 101 is formed of an alloy such as gold-tin (AuSn) alloy or gold-nickel (AuNi) alloy and is used as solder for joining a semiconductor laser that is to be placed above.
Such the submount material 100 is used being cut into a plurality of parts. FIG. 5A is a view showing a state of the submount material 100 being cut, and FIG. 5B is an enlarged view of a section Yin FIG. 5A. The submount material 100 is extremely hard and thus a burr hardly occurs, whereas the plating layer 101 is a soft metal layer and thus a bur 103 may occur when being cut.
When such the burr 103 occurs, a problem in which the burr 103 obstructs a part of light emitted from the semiconductor laser may arise. Also, the burr may become an obstruction, which may deteriorate accuracy of placing of the semiconductor laser and, furthermore, may cause a problem of falling off of the burr. For these reasons, a method in which a burr does not occur when cutting the submount material 100 is required.
As a countermeasure, there is a method in which a non-plated region 105 is formed at a cutting part of the plating layer 101 as shown in FIG. 6A. Forming a non-plated region 105, so-called pullback, at the cutting part in this way can prevent a burr generated at the cutting part of the plating layer 101 as shown in FIG. 6B.
FIG. 7 is a view showing a state in which a semiconductor laser 111 is fixed on a submount 109 formed with such a pullback and the semiconductor laser 111 and an optical fiber 107 are optically coupled. As mentioned above, the non-plated region 105 is formed over a predetermined range from an end of the submount 109. That is, the plating layer 101 is a part other than the non-plated region 105 and is disposed at a position that is a predetermined distance away from the end of the submount 109.
An electrode layer 111a of the semiconductor laser 111 is fixed at a position that substantially coincides with the plating layer 101 on the submount 109. That is, the semiconductor laser 111 is fixed at a position that is a predetermined distance away from the end of the submount 109. Joining approximately the whole lower surface of the semiconductor laser 111 with the submount 109 (the plating layer 101) allows heat from the semiconductor laser 111 to efficiently transmit to the submount 109, and thus high cooling effects can be obtained.
On the other hand, to optically couple the semiconductor laser 111 and the optical fiber 107 directly, it is necessary that a tip end of the optical fiber 107 is close to the semiconductor laser 111. However, as mentioned above, since the semiconductor laser 111 is set back from the end of the submount 109, the optical fiber 107 may interfere with the submount 109 (Z in the drawing).
However, as mentioned above, if the electrode layer 111a of the semiconductor laser 111 is fixed so as to protrude from the plating layer 101, it is impossible to successfully transmit the heat from the semiconductor laser 111 to the submount 109. Thus, it is required that a position of the electrode layer 111a of the semiconductor laser 111 coincides with a position of the plating layer 101. Also, without forming the non-plated region 105, burrs may occur as mentioned above.